The long range goal of this project is to determine the mechanism by which glucose regulates gene expression in the Saccharomyces yeasts. The expression of a wide variety of genes is repressed by glucose. These include: the enzymes of mitochondrial biogenesis, of gluconeogenesis and of sugar fermentation enzymes (such as invertase, galactokinase and maltase). The project will take three major pathways: (1) A genetic analysis of glucose repression will be undertaken. a) The following classes of mutants will be isolated: 1) pleitropic glucose repression insensitive mutants; and 2) mutants affecting only the glucose repression sensitivity of maltase. These will be obtained using either glucosamine selection or Beta-galactosidase fusion plasmids containing glucose repression sensitive controlling elements. b) We will investigate the mode of action of the GLR1 (HXK2) locus in glucose repression. (2) Saccharomyces strains able to ferment maltose contain one or more of a series of MAL loci called MAL1, MAL2, MAL3, MAL4 and MAL6. We plan to undertake a comparative study of the genetic organization of these loci. (3) The MAL6 locus coding for the enzymes of maltose fermentation has been cloned. We will study the transcripts originating from this locus and their regulation. This will include the kinetics of maltose induction and glucose repression of the glucose sensitive transcripts and sequencing of the 5 feet-upstream controlling elements of each transcript.